Measuring the Virial Factor in SDSS DR7 AGNs with Redshifted H$\beta$ and H$\alpha$ Broad Emission Lines

Abstract

Under the hypothesis of gravitational redshift induced by the central supermassive black hole, and based on line widths and shifts of redward shifted H$\beta$ and H$\alpha$ broad emission lines for more than 8000 SDSS DR7 AGNs, we measure the virial factor in determining supermassive black hole masses. The virial factor had been believed to be independent of accretion radiation pressure on gas clouds in broad-line region (BLR), and only dependent on inclination effects of BLR. The virial factor measured spans a very large range. For the vast majority of AGNs ($>$96%) in our samples, the virial factor is larger than $f=1$ usually used in literatures. The $f$ correction makes the percent of high-accreting AGNs decrease by about 100 times. There are positive correlations of $f$ with the dimensionless accretion rate and Eddington ratio. The redward shifts of H$\beta$ and H$\alpha$ are mainly the gravitational origin, confirmed by a negative correlation between the redward shift and the dimensionless radius of BLR. Our results show that radiation pressure force is a significant contributor to the measured virial factor, containing the inclination effects of BLR. The usually used values of $f$ should be corrected for high-accreting AGNs, especially high redshift quasars. The $f$ correction increases their masses by one--two orders of magnitude, which will make it more challenging to explain the formation and growth of supermassive black holes at high redshifts.